The conclusion that can be drawn about the landform on Earth and on Mars is the third option: A few landforms are much larger on Mars than on Earth.
That is the reason why Mars is called "a bit of a show-off" at the end of the text. We all know about Grand Canyon: it's a majestic Canyon in America, visited by people all over the world who marvel at its depth (over 1 mile), length (277 miles) and width (18 miles). Mars has the Mariner Valley, however, whose proportions are gigantic - "Mariner Valley is as long as the continental United States and four miles deep." That landform is clearly much larger than the one we have here on Earth. Thus, the third option is most likely to be the correct one.
